Effect of recombinant human thyroid stimulating hormone on radioactive iodine uptake by thyroid carcinoma in dogs

The high doses of radioiodine-131 (¹³¹I) and, subsequently, the high radioactive burden for dog and environment warrants optimization of ¹³¹I therapy in dogs with thyroid carcinoma (TC).

To evaluate the effect of a revised protocol with recombinant human thyroid stimulating hormone (rhTSH) on tumor radioactive iodine uptake (RAIU) in dogs with TC.

Nine client-owned dogs diagnosed with TC.

A prospective cross-over study in which tumor RAIU was calculated and compared at 8 hours (8h-RAIU) and 24 hours (24h-RAIU) after injection of radioactive iodine-123 (¹²³I), once with and once without rhTSH (ie, 250 μg, IM, 24 and 12 hours before ¹²³I) in each dog. Simultaneously, serum total thyroxine (TT4) and TSH were measured at baseline (T₀), and 6 (T₆), 12 (T₁₂), 24 (T₂₄), and 48 hours (T₄₈) after the first rhTSH administration.

Tumor RAIU was significantly higher at 24 hours with rhTSH compared to no rhTSH (mean difference = 8.85%, 95% CI of [1.56; 16.14]; P = .03), while this was non-significant at 8 hours (mean difference = 4.54%, 95% CI of [0.35; 8.73]; P = .05). A significant change of serum TT4 (median difference T₂₄ - T₀ = 35.86 nmol/L, interquartile range [IQR] = 15.74 nmol/L) and TSH (median difference T₂₄ - T₀ = 1.20 ng/mL, IQR = 1.55 ng/mL) concentrations occurred after administration of rhTSH (P < .001).

Recombinant human TSH could optimize ¹³¹I treatment in dogs with TC by increasing tumor RAIU and thus ¹³¹I treatment efficacy.